Adjustable shave assembly



Dec. 10, 1963 J. G. MOKENNA ADJUSTABLE SHEAVE ASSEMBLY 2 Sheets-Sheet 1 Filed June 21, 1962 5 6 R 6 4 mm 7 w W e e M m7m \\\I/ I 1N1 1/ 7 m0" 6., 4 m 4 w 5 aw w a a 5 w u a Dec. 10, 1963 J. G. MCKENNA ADJUSTABLE SHEAVE ASSEMBLY 2 Sheets-Sheet 2 Filed June 21, 1962 w V b w. W. w w v a I m.. u.r 00010 N a u .M a m r J INVENTOR. g/Zcz 6. Mel sum? BY W 47f }/VEK5 United States Patent 3,113,467 ADJUSTABLE SHEAVE ASSEMBLY Jack G. McKenna, Glendale, Califi, assignor to Mormac Mtg. (30., line, Huntington Park, Calif, a corporation of California Filed June 21, 1962, Ser. No. 204,168 Claims. (Cl. 74-242149 This invention relates to chain saws, and more particularly to an improved adjustable sheave assembly for a heavy duty saw of this ty e.

A conventional chain saw includes basically an elon gated guide plate and a continuous chain which runs in grooves or tracks formed in the edges of the plate. Power is normally applied to the chain by a sprocket located at one end of the guide plate. At the opposite end of the plate, a sheave or pulley wheel assembly is provided in order to achieve smooth running of the chain around the bend.

It is desirable for several reasons that the assembly include means to adjust the sheave longitudinally relative to the guide plate. One such reason is that this enables the tension on the chain to be conveniently adjusted to the desired level. Moreover, it facilitates removal of the chain from the guide plate when it is desired to sharpen or replace it.

Another desirable characteristic of a sheave assembly of the subject type is that the sheave be mounted in such a manner that the chain can yield somewhat when increased resistance to sawing is temporarily encountered. It will be appreciated that if such yielding is not provided for, the chain is likely to break in a situation, for example, where a knot is encountered.

Sheave assemblies presently available for accomplishing these desirable results have not been entirely satisfactory. One specific problem has been that the sheave has not been supported in such a manner as to run freely under all operating conditions. As a consequence, it binds and may result in damage to the chain in addition to loss of efficiency of the saw. Another problem is that heretofore no satisfactory means have been provided for quickly and easily adjusting the sheave in its mounting to vary the tension on the chain.

In view of the foregoing, it is a primary object of the invention to provide a sheave assembly in which the sheave is supported in such a manner as to run free under virtually all operating conditions.

Another object is to provide a device of the type described, characterized in that the sheave may be quickly and easily adjusted in its mounting, and in that it is yieldably movable in its mounting so as to accommodate temporarily increased tension in the chain.

A further object of the invention is to provide an assembly of the type described having the majority of the moving parts encased in closed units of the housing to protect them from damage and interference from dirt and debris.

It is another object of the invention to provide a sheave assembly which is strong and durable and trouble-free in operation, yet which is relatively simple in construction.

These and other objects, features, and advantages of the invention will be better understood by referring to the following detailed description taken in conjunction with the accompanying drawings in which:

FIGURE 1 is a perspective view of a chain saw mounting adjacent one end the sheave assembly of the invention;

FIGURE 2 is a side elevational view of the sheave assembly illustrating the manner in which it is connected to the guide plate of the saw:

FIGURE 3 is a horizontal section taken on the line 3-3 of FIGURE 2;

FIGURE 4 is a vertical section taken on the line 4-4 of FIGURE 3; and

FIGURE 5 is an exploded view in perspective illustrating the parts of the sheave assembly which cooperate to adjustably mount the sheave relative to the guide plate of the saw.

Referring to the drawings, and in particular to FIG- URE 1, numeral 10 indicates generally the assembly of the invention. It is illustrated in conjunction with a conventional chain saw 12, which may be seen to include a guide plate 14 with a groove or track 15 along its opposite horizontal edges for receiving a continuous chain 16. The chain is powered by suitable means, here comprising an engine 17 located at the end of the plate 14 opposite the assembly 10. The details of the constructions and arrangements of the saw parts, such as the guide plate 14 and engine 17, form no part of the present invention. Accordingly, they are: only briefly described in order to clarify the manner in which the assembly 10 is used.

The assembly 14 includes a housing or frame 18 com prised of a pair of separate and virtually identical units 29. In the illustrative case, the units 20 are formed of cast iron. However, other forming methods and materials may, of course, be used to advantage.

Each such housing unit 20 is elongated and provided with a rearward mounting section 22 and an integral forward support section 24 which tapers down in vertical width from the rear toward the front. Further, each is formed with a flat inside surface 26 for mounting purposes and an irregular outside surface 28 in order to provide the necessary space for certain internal cavities and still to conserve material. Referring to FIGURES 3 and 4, it may be seen that a chamber 39 is provided in the mounting section 22 having an opening at the inside surface 26. Extending forwardly from the chamber Bil through the support section 24 is a longitudinal bore 32. A portion of the bore 32 is open at the inside surface 26 by virtue of a longitudinally extending slot 34 (FIGURE 4) in the support section 24.

In order to close each chamber 30, a cover plate 36 corresponding in shape to the mounting section 22 is removably secured to its respective unit 20. The cover 36 is secured in the present case to the inside surface 26 by means of screws 38.

In mounting the housing 18 on the guide plate 14, the mounting sections 22 of the units are clamped together with the end of the plate between them. Bolts 40 extend through the unit occupying the lower position in FIGURE 3, as well as through the cover plates 36, and are received in threaded bores 42 in the outer unit. By virtue of the guide plate 14 and the cover plates 36 being positioned between the inside surfaces 26 of the units, they are spaced apart a distance equal to the combined thicknesses of those plates 14 and 36. When so mounted, the longitudinal bores 32 in the support sections 24 are parallel to one another and to the longitudinal axis of the guide plate 14. Further, the slots 34 in the support sections are positioned directly opposite and facing one another.

A sheave 44 with a groove 46 in its peripheral edge for receiving the chain 16 is rotatably mounted on the housing 18. As was explained above, the primary purpose of the sheave 44 is to enable the chain 16 to run freely around the end of the guide plate 14. An assembly for mounting the sheave 44 in the desired manner includes a pair of shaft supports 50, an associated pair of mounting sleeves 52 and a shaft 54, as may be seen in FIGURE 5.

Each of the supports 50 is cylindrical in shape and is slidably received in a corresponding one of the longitudinal bores 32 in the support section 24 adjacent its forward end. As is also shown in FIGURE 5, a bore 56 extends transversely into each of the supports 50 and is internally threaded for the reception of a correspondingly threaded end portion of its mounting sleeve 52. When the supports 50 are positioned within their bores 32 and the mounting sleeves 52 are threadedly engaged in the bores 56, the sleeve members may be seen in FIGURE 3 to project inwardly through the longitudinal slots 34 in the support sections. Because of this, the supports 50 are held against rotational movement, and their longitudinal movement is limited to the extents of the slots 34.

In an assembled condition, the ends of the shaft 54 extend into the mounting sleeves. Preferably, in order to prevent rotation of the shaft 54, one of its ends is non-circular in shape and is received in a cavity of corresponding shape in the mounting sleeve. Referring to FIGURE 5, it may be seen that in the illustrative case, the end 54a of the shaft is square and receivable in a like cavity in its mounting sleeve.

To minimize friction, the sheave 44 is rotatably mounted on the shaft 54 by means of a ball bearing 58. As illustrated in FIGURE 3, the bearing has its inner race 60 received in close fit on the shaft 54 and confined between the inner ends of the mounting sleeves 52. Conversely, the outer race 62 of the bearing is press fit in a central axial bore 64 in the sheave 44.

It will be noted that, when the sheave 44 is in position for use, it has its axis of rotation arranged parallel to and aligned with the central longitudinal axis of the guide plate 14. The external diameter of the sheave 44 is, as illustrated in FIGURES 1 and 2, preferably slightly less than the vertical width of the plate 14. Making the parts of such relative sizes, permits the chain to run smoothly out of the track at one horizontal edge of the plate, around the sheave 44 and back into the track at the opposite edge of the plate.

In order to longitudinally adjust the initial position of the sheave 44 relative to the housing and, at the same time, limit the extent of its rearward movement, adjustment means are provided. Such means include essentially a pair of cams 66, associated followers 68, and an adjustment shaft 70. Each cam 66 is mounted within the chamber 30 of its unit 20, with proper centering therein being accomplished by cylindrical mounting flanges 72 on the cams. As is best shown in FIGURE 3, each flange 72 is received at one of its ends in a mating cylindrical bore 73 in the housing and abuts the cover plate 36 at the opposite end. The mounting flanges 72 of the cams are centrally bored, as at 74, for the reception of the shaft 70. Preferably, to key the shaft 70 to the cams 66 and insure that the cams move in unison, the shaft 70 and the cooperating bore 74 are made non-circular in shape, as shown in FIGURE 5. To facilitate movement of the shaft 70, it is provided with a T-handle 76 at one of its ends.

The followers 68 are cylindrical in shape for slidable mounting within respective ones of the longitudinal bores 32 in the support sections 24. Each follower is positioned adjacent the rearward end of its bore 32 and adapted to engage the cam 66. To allow for movement of the cam into the bore 32, the support section is provided with a vertical slot 77 at the rearward end of the bore 32, as illustrated in FIGURES 3 and 4.

It will be recalled from the introductory discussion, that it is desirable to permit some yieldable movement of the sheave 44 relative to the housing 18. To this end, compression springs 78 are provided between the followers 68 and supports 50 to yieldably resist movement of these members toward one another. In order .to keep the springs 78 properly centered in the bores 32, a shaft 80 of reduced diameter extends forwardly 4 from each follower 68 and is received in an axial bore 82 in the associated support.

Adjustment of the longitudinal position of the sheave 44 is achieved by merely rotating the adjustment shaft 70 with the aid of the handle 76. By way of example, counterclockwise rotation of the shaft 70 in FIGURE 4 rotates the cams 66 keyed thereto and, in turn, advances the followers 68 proportionately in their bores 32. Along with this movement to the followers 68, the assembly 48 including the sheave 44 is moved to the right in the drawings by virtue of its operative connection to the followers. Conversely, clockwise movement of the shaft 70 in FIGURE 4 permits the sheave 44 to move to the left. It will be appreciated that the mounting arrangement is such that the sheave 44 is free to move forwardly, i.e. to the right in the drawings, relative to the housing to the full extent permitted by the slots 34. However, under actual operating conditions, such movement is limited by the chain 16 which in tension extends around the sheave 44 and urges it rearwardly. Rearward movement of the sheave 44, i.e. to the left in the drawings, is limited by the position of the cams 66, with some yieldable movement permitted by compression of the springs 78.

In order to maintain the earns 66 in a given position of adjustment, suitable means are provided on the cam and housing 18. Such means comprise a plurality of bores 84 in each of the cams and cooperating locking screws 86 on the units 20 of the housing. The bores 84 are located at equidistant spacing along a curve defined by a common radius from the axis of rotation of each of the cams 66. Referring to FIGURE 3, it may be seen that each of the screws 86 includes a pin 88 at one end engageable in an aligned one of the bores 84, a threaded intermediate portion 90 received in a correspondingly threaded bore 92- in the housing, and a knurled head 94 accessible externally of the housing. Preferably, in order to preclude the screws from backing out of locking engagement within their cams, compression springs 102 are disposed between the outside surfaces of the housing and the head 94 of the screw.

To ready the assembly 10 of the invention for use, each unit 20 of the housing is first assembled with its various internal parts. In this regard, it will be noted that the cams 66, followers 68, springs 78 and supports 50 are all enclosed within the housing and thereby protected from interference by dirt and debris. As another step, the adjustment shaft 70 is inserted through the bore 74 in the cam-mounting flange 72 in the unit 20 occupying the lower position in FIGURE 3. The shaft 70 is locked in assembly with that unit by a conventional snap ring 96 in a groove (not shown) in the shaft. Similarly, after the sheave 44 has been assembled on the shaft 54, the square shaped end 54a of shaft 54 is inserted into its associated mounting sleeve 52 and secured in assembly therewith by the ring-groove arrangement 100 (FIGURE 5). That mounting sleeve 52 with the sheave 44 and shaft 54 attached as a sub-assembly is next threaded into the bore 56 in the support 50 of its housing unit 20, here comprising the lower unit in FIGURE 3, to attach the sub-assembly to that unit. Likewise, the other mounting sleeve 50 which at this stage is free of the shaft is threadedly engaged in the support 50.

It will be appreciated that, when in this configuration, the assembly of the invention embodies only two separate parts, the various individual components being connected to one or the other of those parts. This is an important advantage, as it is frequently necessary to remove the assembly *10 from the guide plate under adverse conditions in order to repair or replace the latter. By virtue of having essentially only two separate parts, the possibility of misplacing or losing parts during such operations is virtually eliminated.

To mount the assembly 10 on the guide plate 14, the adjustment shaft 70 is inserted through a bore 104 in the plate and then through the bore in the mounting flange of the other cams 66. Simultaneously, the free end of the shaft 54 is inserted in its associated mounting sleeve 50. Finally, the four mounting bolts 40 are inserted through one housing unit 20 and threadedly engaged in the other to clamp these two units to the guide plate 14. It will be understood that by virtue of the shaft 70 and bores 74 being non-circular in shape, the cams are automatically aligned with respect to one another.

In use, assuming the chain 16 to initially be engaged in the sheave 44, as in FIGURE 1, the chain runs out of the track 15 at one horizontal edge of the guide plate 14, around the rotatable sheave 44 and back on to the track at the opposite edge of the plate. Should it be desired to vary the tension on the chain 16, the locking screws 36 are merely backed off to remove the pins 88 from the bores 84 in the cams 66, whereupon the shaft 70 is rotated in the appropriate direction. In the event that it is desired to remove the chain 16 from the sheave 44 and guide plate 14, the shaft 70 is then rotated to move the cams 66 the maximum extent in the clockwise direction. This permits the sheave 44 to move the maximum possible extent to the left in the drawings. After replacement of the chain 16 on the sheave 44 and adjustment to achieve the desired tension, the locking screws 36 are retightened to engage in the bores then aligned with them.

A particularly advantageous feature of the invention is that the shaft 54 is supported in an identical manner on both sides of the sheave 44. Accordingly, the assembly is maintained from binding both during adjustment, as well as during operation in a case where temporarily increased tension is applied to the chain. Thus, the useful life of the chain is materially lengthened. Moreover, the operator is able to quickly and easily effect adjustment of the tension on the chain.

Although one embodiment of the invention has been illustrated and described with a considerable degree of particularity, it will be understood that various changes in the details of the construction and arrangement of the various parts may be made Without departing from the spirit and scope of the invention.

I claim:

1. A sheave assembly for use with a chain saw having an elongated guide plate and a chain adapted to run along the edges of said plate, comprising:

a housing with forward and rearward ends, said housing being adapted for mounting at its rearward end on said guide plate and being formed at its forward end with a pair of spaced apart support sections;

a pair of shaft supports slidably mounted, one each, on said sections for longitudinal movement forwardly and rearwardly relative thereto;

a shaft extending between said supports;

a sheave rotatably mounted on said shaft at a location intermediate said supports;

means carried by said housing for yieldably resisting rearward movement of said supports;

a pair of independent adjustment means on said housing associated, one each, with said supports for establishing the positions of said supports relative to said housing;

and means on said housing and operable from the exterior thereof for operating said pair of adjustment means coincidentally.

2. A sheave assembly for use with a chain saw having an elongated guide plate and a chain adapted to run along the edges of said plate, comprising:

a housing with forward and rearward ends, said housing being adapted for mounting at its rearward end on said guide plate and being formed at its forward end with a pair of spaced apart support sections;

cams mounted on said support sections for movement relative thereto;

cam followers mounted on said support sections at locations spaced forwardly of said cams, each of said followers being engageable with a respective one of said cams and movable forwardly and rearwardly relative to said housing;

shaft supports carried by and movable forwardly and rearwardly relative to said sections, each of said supports being associated with and positioned forwardly of a respective one of said followers;

a shaft extending between said supports;

a sheave on said shaft intermediate said supports;

spring means between said associated followers and supports for yieldably resisting movement of them toward one another;

and means on said housing and operatively connected to said cams for moving them coincidentally.

'3. A sheave assembly for use with a chain saw having an elongated guide plate and a chain adapted to run along the edges of said plate, comprising:

a housing including a pair of separable units having forward and rearward ends, said units being clamped together at their rearward ends with said guide plate therebetween;

cams rotatably mounted on said units;

cam followers mounted on said units at locations spaced forwardly of said cams, each of said followers being engageable with one of said cams and movable longitudinally of its unit;

shaft supports carried by and movable longitudinally of said units, each of said supports being positioned forwardly of its respective follower;

springs carried by said units intermediate said followers and supports for yieldably resisting movement of the latter members toward one another;

a shaft extending between said supports;

a sheave rotatably mounted on said shaft;

means on said housing and operable from the exterior thereof for coincidentally rotating said cams;

and means on said housing for locking said cams in adjusted position.

4. A sheave assembly for use with a chain saw having an elongated guide plate and a chain adapted to run along the edges of said plate, comprising:

a housing including a pair of separable units, each having forward and rearward ends and being provided with a mounting section with a chamber adjacent its rearward end and a longitudinally bored support section adjacent its forward end with a longitudinally extending slot in the side wall opening the bore to the exterior, said units being clamped together adjacent their rearward ends with said plate therebetween to position said support sections in spaced apart relation and with their longitudinally extending slots opposite and facing one another;

cams movably mounted in the chambers of said mounting sections;

cam followers slidably mounted on the longitudinally bored sections of said units at locations spaced forwardly of said cams, each of said followers being engageable with its respective cam;

shaft supports slidably mounted in said support sections at locations spaced forwardly of said followers;

means in said support sections intermediate said followers and supports for yieldably resisting movement of them toward one another;

shaft means connected to said supports and extending through the longitudinal slots in said units;

a sheave rotatably mounted on said shaft;

and means operatively associated with said cams and operable from the exterior of said units for coin c identally moving said cams.

5. A sheave assembly for use with a chain saw having an elongated guide plate and a chain adapted to run along the edges of said plate, comprising:

a housing with forward and rearward ends, said housing being adapted for mounting at its rearward end on said guide plate and being formed at its forward s, 1 1 3,467 Z 8 end with a pair of spaced apart support sections; means on said housing for operating said adjustment a pair of shaft supports slidably mounted, one each, on means coincidentally; I

said sections for longitudinal movement forwardly and a pair of locking means on said housing for lockand rearwardly relative thereto; ing respective ones of said pair of adjustment means a shaft extending between said supports; 5 relative to said housing. a rotatable sheave on said shaft intermediate said supports; References Cited in the file of this patent a pair of independent adjustment means supported by said housing and associated, one each, with said supports, said adjustment means being movable for 10 adjustably establishing the longitudinal positions of said supports relative to said housing;

UNITED STATES PATENTS 

1. A SHEAVE ASSEMBLY FOR USE WITH A CHAIN SAW HAVING AN ELONGATED GUIDE PLATE AND A CHAIN ADAPTED TO RUN ALONG THE EDGES OF SAID PLATE, COMPRISING: A HOUSING WITH FORWARD AND REARWARD ENDS, SAID HOUSING BEING ADAPTED FOR MOUNTING AT ITS REARWARD END ON SAID GUIDE PLATE AND BEING FORMED AT ITS FORWARD END WITH A PAIR OF SPACED APART SUPPORT SECTIONS; A PAIR OF SHAFT SUPPORTS SLIDABLY MOUNTED, ONE EACH, ON SAID SECTIONS FOR LONGITUDINAL MOVEMENT FORWARDLY AND REARWARDLY RELATIVE THERETO; A SHAFT EXTENDING BETWEEN SAID SUPPORTS; 